Method, Apparatus, and Program for Processing Stereo Image

1. A method for processing a stereo image, for measuring parallax by making a stereo-correspondence search between a base image taken with a first imaging device and a reference image taken with a second imaging device, comprising the steps of: setting a specified area of a base window with reference to an object point for obtaining a corresponding point in the base image; setting a reference window having a same size as that of the base window in the reference image; evaluating a difference between patterns of the base window and the reference window while scanning the reference window along an epipolar line in the reference image which corresponds to the object point; determining a position of the reference window having a minimum difference as a stereo corresponding point; measuring the parallax by a difference between a position of the base window and a position of the reference window when the stereo-corresponding point is determined; calculating a reliability of the parallax by first reliability based on a sharpness of a peak of an evaluation-value distribution of the difference of patterns between the base window and the reference window obtained by scanning the reference window and second reliability based on a shape of the peaks; and outputting a value of the reliability of the parallax together with a value of the parallax.

2. The method for processing a stereo image according to claim 1 , further comprising the steps of: calculating an inter-frame difference between a frame processed immediately before and a current frame in the base image; making a stereo correspondence search only for a changed area determined to be changed between the frames and an unsearched area; and outputting an immediately preceding stereo-correspondence search result for an unchanged and searched area.

3. The method for processing a stereo image according to claim 1 , further comprising the steps of: enlarging a size of the base window and the reference window during the stereo-correspondence search, for the area with lower reliability of parallax than a specified value among the unchanged and searched area; repeating the stereo-correspondence search continuously following the stereo-correspondence search of the changed-area and the unsearched area; and updating information on the parallax of the area and the reliability of the parallax when the reliability is improved.

4. The method for processing a stereo image according to claim 1 , further comprising the steps of: calculating the search-starting-position coordinates in the reference image which corresponds to each pixel in the base image, in advance, on the basis of tilt angles of optical axes of the first imaging device and the second imaging device; holding a correspondence relationship between the position coordinates of each pixel in the base image and the search-starting-position coordinates in the reference image which correspond to each pixel in the base image as a table; and making a stereo-correspondence search from a search starting position in the reference image which is obtained by referencing the table.

5. A stereo-image processing apparatus for measuring parallax by making a stereo-correspondence search between a base image taken with a first imaging device and a reference image taken with a second imaging device, comprising: first setting means for setting a specified area of a base window with reference to an object point for obtaining a corresponding point in the base image; second setting means for setting a reference window having the same size as that of the base window in the reference image; evaluation means for evaluating a difference between patterns of the base window and the reference window while scanning the reference window along an epipolar line in the reference image which corresponds to the object point; determination means for determining a position of the reference window having a minimum difference as a stereo corresponding point; measurement means for measuring the parallax by a difference between a position of the base window and a position of the reference window when the stereo-corresponding point is determined; calculation means for calculating a reliability of the parallax by first reliability based on a sharpness of a peak of an evaluation-value distribution of the difference of patterns between the base window and the reference window obtained by scanning the reference window and second reliability based on a shape of the peaks; and output means for outputting a value of the reliability of the parallax together with a value of the parallax.

6. A computer-readable storage medium having stored thereon, a computer program for controlling a stereo-image processing apparatus for measuring parallax by making a stereo-correspondence search between a base image taken with a first imaging device and a reference image taken with a second imaging device, allowing the stereo-image processing apparatus to execute the steps of: setting a specified area of a base window with reference to an object point for obtaining a corresponding point in the base image; setting a reference window having the same size as that of the base window in the reference image; evaluating a difference between patterns of the base window and the reference window while scanning the reference window along an epipolar line in the reference image which corresponds to the object point; determining a position of the reference window having a minimum difference as a stereo corresponding point; measuring the parallax by a difference between a position of the base window and a position of the reference window when the stereo-corresponding point is determined; calculating the reliability of the parallax by first reliability based on a sharpness of a peak of an evaluation-value distribution of the difference of patterns between the base window and the reference window obtained by scanning the reference window and second reliability based on a shape of the peaks; and outputting a value of the reliability of the parallax together with a value of the parallax.